Blades for hand held power operated shears

ABSTRACT

A hand-held power-operated blade-actuating or other work member actuating device, especially useful as shears for processing comestible products such as fowl. A servo mechanism and linkage connected with a movable blade and a finger control causes controlled powered movement of the blade in coordination with the finger control. A fixed blade and a pivoted blade are insertable and removable as a unit from a hand-held frame in which the fixed blade is restrained against rotation relative to the frame. The blades and frame are constructed so the blades are insertable or removable only when closed. In a preferred embodiment the fixed blade is retained in part by two load bearing pins extending from the frame and located substantially diametrically opposite each other relative to the pivot axis of the movable blade.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This is a continuation-in-part application of copendingapplication Ser. No. 08/330,183 filed Oct. 27, 1994 which is adivisional application of Ser. No. 08/132,526 filed Oct. 6, 1993, nowU.S. Pat. No. 5,375,330.

BACKGROUND OF THE INVENTION

[0002] 1. Technical Field

[0003] The present invention relates generally to improved poweroperated shears that are useful for industrial cutting applications. Inparticular, the improved shears of the present invention are suitablefor use in the food processing industry to cut and trim meat, andespecially to cut poultry.

[0004] 2. Description of the Prior Art

[0005] Hand held manually operated conventional scissors have been usedfor cutting and trimming meat and other food products. Conventionalscissors also have been used in a variety of other industries forcutting sheet material, such as cloth, textiles or thin metals. It wasnecessary for an operator of the conventional scissors to use arelatively large cutting effort and often the operator's wrist was at anunnatural orientation. Repetitive use at such orientation and largecutting effort could cause injury to the operator's wrist. To reduce theeffort needed to operate such conventional scissors, power operatedshears have been devised.

[0006] Most known power operated hand held shears have variousshortcomings. For example, most such shears do not have a similarphysical arrangement to conventional scissors, the blade movement cannotbe controlled to the same extent and in the same way as conventionalmanually powered shears, the blades are not easily replaced and theblades, if replaceable, are not reliably retained in the shears towithstand repeated heavy loading.

[0007] Thus, a need exists for power operated or power assisted cuttingshears that are arranged, operated and controlled in a manner similar tothat of conevntional manually-operated scissors, and have easilyreplaceable blades that can withstand the repeated heavy loading thatpower operated shears used in a commercial setting will encounter,

SUMMARY OF THE INVENTION

[0008] The present invention is directed to replaceable blades for handheld power operated shears used in a commercial setting. The poweroperated shears overcome the shortcomings of the known power operatedshears mentioned above and others by being closely similar in physicalarrangement and operation to that of conventional manually operatedscissors. Other operating advantages of the hand held power operatedshears of the present invention include a controllable rate of closingof blades, a controllable extent of closing, easily replaceable bladesand a reliable load bearing mounting for one of the blades.

[0009] The present invention is also directed to hand held poweroperated tools, and more particularly shears. While the invention willbe described in connection with the preferred shears, it will beunderstood that other work members for accomplishing a desired task canbe arranged and operated by a tool in the same or similar manner as theshear blades.

[0010] The shears include first and second blades for cutting aworkpiece upon relative pivotal movement from a first open positiontowards a second closed position. A frame supports the blades forrelative pivotal movement about an axis. A first handle and a secondrelatively pivotable handle are provided. One of the handles issupported for pivoting about an axis independently of the blades. Thepivoting handle extends in a direction relative to the axis opposite thesecond blade. The other of the handles extends in a direction oppositethe first blade relative to the axis. An actuator pivots the secondblade relative to the first blade to impart a cutting action betweenblades. A servo mechanism is controlled by movement of the second bladeand pivoting handle to control operation of the actuator to pivot thesecond blade relative to the first blade in coordination with movementof the pivoting handle.

[0011] The blades are readily replaceable. The blades are supported forrelative pivotal movement. One blade is constructed to be fixed in asupporting frame. The other blade is constructed to be pivotablerelative to the frame and first blade. The pivotable blade has anactuating portion extending in an opposite direction from the pivot froma cutting portion of the blade at an obtuse angle in the range of about120° to 170° relative to a portion of the cutting edge.

[0012] The actuating portion of the pivotable blade has a drive slotthat receives a portion of a drive link connected to a piston rod of thefluid actuator. The length and angle of the actuating portion of thepivotable blade and the distance the slot length extends, as well as thelocation of the pivot, are coordinated with the drive link to allow asize and arrangement of the parts that facilitate locating parts in thearea of the shears that can be accommodated by the palm of theoperator's hand. The length and angle of the actuating portion at thesame time produces relatively high leverage between the blade and thefluid actuator over a cutting excursion of 45 degrees of relativepivoting of the blades. The provision of relatively high leverageassures lower reaction forces at the pivot of the blades. Lower reactionforces allow lower structural weight and longer wear life. Relativelyhigh leverage also allows the use of a relatively slim actuatingcylinder that can provide adequate force using typical shop airpressures.

[0013] The pivotable blade has a heel portion forming a part of theactuating portion. The heel portion has a ride surface facing an opposedsurface of the fixed blade. In one embodiment a part of the opposedsurface of the fixed blade projects toward the ride surface of thepivotable blade, biasing the cutting edges of the blades into mutualcontact where the cutting edges intersect.

[0014] Thus, the invention herein disclosed and claimed is, in itsprincipal broad aspects, directed to a pair of replaceable blades for ahand-held power-operated blade-actuating device. The blades are withouthandles, have cooperating edges for cutting, and the pair comprises afirst blade having a cutting portion and having a mounting portion bywhich the first blade can be fixed relative to a support and a secondblade having a cutting portion and an actuating portion and constructedto be pivoted relative to the support and the first blade at a locationon the second blade between the cutting portion of the second blade andthe actuating portion of the second blade, A surface forms a part of theactuating portion for operatively coupling the second blade to a poweractuator. The actuating portion of the second blade includes a portionthat is located relative to the mounting portion of the first blade andthe support structure when the blades are closed to allow attachment andremoval of the blades as an assembled unit to or from the support, andis located when the blades are open to prevent the attachment or removalof the blades to or from the support. A locating surface on the pair ofassembled blades extends transversely of the general extent of theblades for engaging with a surface of the support that extendstransversely of the general extent of the blades when the blades aremounted on the support.

[0015] The portion of the second blade that allows or preventsattachment or removal of the blades in one preferred embodiment isconstructed to underlie the mounting portion of the first blade when theblades are closed and to extend from behind the mounting portion whenthe blades are not closed, and when extending is obstructed by a surfaceof the support from moving in a direction along which the blades can beremoved from the support.

[0016] In one preferred embodiment a locating surface of the assembledblades is at the pivot between the blades. In another preferredembodiment, a locating surface is provided on a mounting portion of oneof the blades, and in its preferred construction, two apertures areprovided, located to lie on substantially diametrically opposite sidesof the pivot for the blades.

[0017] The invention, in its broad aspects applies to work members otherthan shears or replaceable cutting blades, but otherwise of the generaldescription as above.

[0018] Further features of the present invention will become apparent tothose skilled in the art to which the present invention relates fromreading the following descriptions with reference to the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0019]FIG. 1 is a plan view of hand held power operated shears embodyingthe present invention with the handles and blades in fully closedrelative positions;

[0020]FIG. 2 is a view similar to FIG. 1 with parts in fully openrelative positions;

[0021]FIG. 3 is a partial perspective view of the shears in FIG. 1 withparts removed for clarity illustrating the major movable parts;

[0022]FIG. 4 is a view similar to FIG. 3 illustrating relative positionsof some parts of the shears;

[0023]FIG. 5 is an enlarged perspective view of a frame and handleportion of the shears in FIG. 1;

[0024]FIG. 6 is an exploded perspective view of a portion of the shearsin FIG. 1 illustrating the frame and the blades;

[0025]FIG. 7 is a perspective view of the portion of the shears in FIG.6 with the parts assembled;

[0026]FIG. 8 is an enlarged perspective view of the frame and handle ofthe shears;

[0027]FIG. 9 is an enlarged perspective view of the frame and handle inFIG. 8 viewed from another direction;

[0028]FIG. 10 is a plan view of one replaceable blade of the shears;

[0029]FIG. 11 is a plan view of another replaceable blade of the shears;

[0030]FIG. 11A is a plan view of an alternate embodiment of the bladeillustrated in FIG. 11;

[0031]FIG. 12 is a side view of the blade illustrated in FIG. 11 takenalong the line 12-12 in FIG. 11;

[0032]FIG. 13 is an enlarged view of an axial end portion of the bladein FIG. 12;

[0033]FIG. 13A is a view similar to FIG. 13 illustrating an alternateaxial end portion of the blade;

[0034]FIG. 14 is an exploded perspective view of the major movable partsof the shears in FIG. 1;

[0035]FIG. 15 is a plan view of a fluid power actuator, drive link andblade of the shears;

[0036]FIG. 16 is an enlarged longitudinal cross-sectional view of theservo control valve and safety valve of the shears;

[0037] FIG, 17A-H are schematic longitudinal cross-sectional views ofthe servo control valve in FIG. 16 illustrated with parts in differentoperating positions;

[0038]FIG. 18 is a graph representing the ratio of the change in bladeangle relative to the change in handle angle as a function of therelative angle between the blades;

[0039]FIG. 19 is an enlarged side elevational view of a frame of analternate embodiment and replaceable blades of the invention,illustrating a load bearing mounting arrangement between one of theblades and the frame;

[0040]FIG. 19A is a top view of the blades in FIG. 19;

[0041]FIG. 20 is an exploded perspective view of the frame and blades inFIG. 19, better illustrating the load bearing mounting arrangement;

[0042]FIG. 20A is a detailed view partly in section of a pivotingconnection for the blades;

[0043]FIG. 21 is a plan view of an alternate embodiment of replaceableblades;

[0044]FIG. 21A is a top view similar of the blades in FIG. 21;

[0045]FIG. 22 is a plan view of another alternate embodiment ofreplaceable blades;

[0046]FIG. 23 is a plan view of another alternate embodiment ofreplaceable blades;

[0047]FIG. 24 is a plan view of another alternate embodiment ofreplaceable blades;

[0048]FIG. 25 is a plan view of another alternate blade embodiment; and

[0049]FIG. 26 is a top plan view of the frame of FIG. 19, with theorientation reversed.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

[0050] Overview

[0051] Hand held power operated shears 20, embodying the presentinvention, are illustrated in FIG. 1. The shears 20 include a pivotableblade 22 which is reciprocable relative to another blade 24 between thefully open position illustrated in FIG. 2 and the fully closed positionillustrated in FIG. 1. A cutting or shearing action is provided betweenthe cutting edges 42, 44 (FIG. 2) of the blades 22, 24, respectively,during movement of the pivotable blade 22 relative to the blade 24 fromthe open position towards the closed position. An advantage of thepresent invention is that the shears 20 appear, and operate in a manner,very similar to conventional manually powered scissors. Thisconventional type of operation is advantageous because little or notraining or adaptation to the power operated shears 20 is required.

[0052] The blades 22, 24 are supported in a frame 62 about an axis AA.The frame 62 supports the blade 24 in a fixed relative position. Theblade 22 is pivotable relative to the frame 62 and relative to the fixedblade 24 about the axis AA. A thumb handle portion 64 is formed in theframe 62 for receiving an operator's thumb to support and control theshears 20. A finger loop handle 66 is supported in the frame 62 forpivotal movement. Thus, the blades 22, 24 and the finger loop handle 66are all supported on the frame 62 along the axis AA. In response topivotal movement of the handle 66 relative to the frame 62 and thumbhandle portion 64, the blade 22 is power driven to pivot relative to theblade 24.

[0053] The frame 62 also supports a servo mechanism 82 (FIGS. 1-5) forcontrolling the power applied to pivot the blade 22. The servo mechanism82 includes a servo control valve 84 (FIG. 3), an optional safety valve86, an actuator 88, a drive link 102, and a feedback linkage 104. Thedrive link 102 transmits power from the actuator 88 to the pivotableblade 22. The feedback linkage 104 determines the difference between theposition of the finger loop handle 66 relative to the frame 62 and theposition of the pivotal blade 22 relative to the frame. The feedbacklinkage 104 communicates the difference between the position of theblade 22 and the position of the loop handle 66 to the servo controlvalve 84. The control valve 84 selectively permits or inhibits the flowof a power medium to the actuator 88. The power is preferably providedby a fluid, such as pressurized air. However, it will be apparent thathydraulic or electrical power assist can be used.

[0054] Another mounting arrangement between a modified fixed blade 24Band a modified frame 62B is illustrated in FIG. 19. The mountingarrangement between replaceable blades 22B, 24B and the frame 62B isdesigned to be secure and reliable, yet easily replaceable, when theblades are to be changed. The modified frame 62B includes a pair of loadbearing pins 63 fixed to and extending transversely from a portion ofthe frame 62B. The pins 63 are located on substantially diametricallyopposite sides of the axis AA about which the blades relatively pivot.The fixed blade 24B includes a pair of openings 67A, 67B formed in itsmounting portion 290B. The load bearing pins 63 are received in the pairof openings and receive the majority of the load between the frame andthe blades occurring during relative pivoting of the blades 22B, 24Bduring a cutting operation.

[0055] Construction

[0056] The pivotable blade 22 is preferably formed from a suitablemetal, such as stainless steel. The cutting edge 42 is formed in theblade 22 by a suitable operation such as by grinding and/or polishing.Preferably, the cutting edge 42 is substantially straight. However, itwill be apparent that the cutting edge 42 may be formed into anysuitable shape necessary to perform a desired cutting function, forexample, a large radius curve or straight portion and a curved tip endportion with a relatively large radius.

[0057] The frame 62 (FIGS. 8 and 9) supports all of the parts of theshears 20. The thumb handle portion 64 is integrally formed in the frame62 for receiving an operator's thumb. The frame 62 also includes arecess 120 (FIG. 8), a recess 122 (FIGS. 6 and 9), exhaust port 129(FIG. 9), an actuator support 124 (FIGS. 8 and 9), valve chambers 126,128 (FIG. 9), a thumb opening 142 and an attachment hook 144. Theattachment hook 144 permits the frame 62 and shears 20 to be connectedduring use to a weight compensating device, such as a constant forcespring. The recess 120 (FIG. 8) in the frame 62 receives the feedbacklinkage 104 and a pivot portion of the finger loop handle 66. A support118 is integrally formed on the frame 62 and projects generallyperpendicularly from a side surface 116 defining a portion of the recess120, The support 118 is received in an opening 119 (FIG. 14) in thepivot portion of the finger loop handle 66 in a close fit relationshipfor pivotal movement about the axis AA. The uncovered recess 120 allowseasy removal of any debris that may enter the recess and contact thefeedback linkage 104 or pivot portion of the finger loop handle 66. Areturn spring 226 (FIG. 14) is located within the recess 120 and engagesboth the finger loop handle 66 and the frame 62. The return spring 226continually biases the loop handle 66 towards a fully open position, asillustrated in FIG. 2.

[0058] A recess portion 130 (FIG. 8) defines a space which is incommunication with the recess 120 and the recess 122 to permitinteraction between the blades 22, 24; the finger loop handle 66; theservo mechanism 82 and the feedback linkage 104. The recess portion 130is located between the recess 120 and thumb handle portion 64. Therecess 130 receives the drive link 102 (FIGS. 4 and 5) therein, Thedrive link 102 is supported for pivotal movement within the recessportion 130 at openings 132 (FIGS. 8 and 9) by a pin 134 (FIG. 14).extending through the opening. The drive link 102 (FIGS. 4 and 5)connects the actuator with the pivotable blade 22. The drive link 102forces the blade 22 to pivot relative to the frame 62 and relative tothe fixed blade 24 in response to movement of the rod 166 (FIG. 14) of apart in the actuator 88.

[0059] The recess 122 in the frame 62 receives the blades 22, 24. Acavity 146 (FIGS. 6 and 9) within the recess 122 extends coaxiallyinside of the support 118 which projects to the recess 120 from thesurface 116. The opening 146 receives a support member 148 on which theblades 22, 24 are supported. The blade 22 is closely fit about thesupport member 148 for pivotal movement about the axis AA, The blade 24is also closely fit on the support member 148. The blade 24 is fixedrelative to the frame 62 by a surface 150 of the blade that engagessurfaces 152, 154 of the recess 122, which prevents movement of theblade relative to the frame 62. The surfaces 152, 154 in the recess 122are located on diametrically opposite sides of the blade 24 relative tothe axis AA to engage the surfaces 150 and 150B of a mounting portion290 (FIG. 11) of the fixed blade 24 in connection with the supportmember 148 to accommodate reaction forces acting on the blade 24. Theblades 22, 24 are illustrated in the fully open position in FIGS. 2 and7. The pivotable blade 22 is disposed at an acute angle W of about 40°to 45° relative to the fixed blade 24. This angle W, however, can bepredetermined and varied for specific job requirements, such as by usinga different servo mechanism 82, blade 22 or frame 62.

[0060] The recess 122 is closed by a latch cover plate 162 (FIGS. 6 and7), after the blades 22, 24 are received therein. The frame 62 and latchcover plate 162 protect the blades 22, 24 from debris entering therecess 122. The latch cover plate 162 includes a body portion 160 forclosing the recess 122 and for preventing the blades 22, 24 and supportmember 148 from movement laterally outwardly of the recess in adirection along the axis AA.

[0061] It will be clear from FIG. 7 that, by virtue of the shape of theopening in which the cover 162 fits and through which the mountingportion 290 and actuating portion 246 must fit to be installed orremoved, the blades must be closed during installation or removal toalign the actuating portion with the opening. This provides a safetyfeature to reduce risk of an operator being cut by the sharp edgesduring handling or by having the blades in an unsafe condition at thetime they are installed and connected to the actuating mechanism.

[0062] The latch cover plate 162 is movable relative to the frame 62 inthe directions indicated by arrows 159 (FIG. 6) formed on the exteriorof the latch cover plate to permit access to the blades 22, 24. Aconnecting portion 157 extends from the body portion 160 to pivotallyand slidably attach the latch cover plate 162 to the frame 62. Theconnecting portion 157 has a slot 157S formed therein for receiving apin 157P. The slot 157S allows the latch plate cover 162 to slide aswell as pivot relative to the pin 157P. The slot 157S has an hour-glassshape across its width so the walls defining the slot are flexible tourge the latch plate cover 162 in one of two directions it can slide totend to retain the latch plate cover in a closed or open position. Thelatch cover plate 162 is free to pivot outwardly of the frame 62 whenthe latch cover plate is axially moved to an open position as indicatedby open arrow 159, by virtue of freeing retaining tabs 151, 153 fromtheir respective receiving slots 151S, 153S.

[0063] A finger grip 155 is provided on a body portion 160 to move thelatch cover plate 162 to an open position permitting access to therecess 122 and blades 22, 24. Each retaining tab 151, 153 includes aramp 151R, 153R which is received in a respective slot 151S, 153S in theframe 62. The ramps 151R, 153R are tapered to permit relatively easyinsertion of the tabs 151, 153 into a slot 151S, 153S and to force thelatch cover plate 162 inwardly towards the recess 122 in a directionalong the axis AA. This assures that the inwardly facing surface of thelatch cover plate 162 engages a bushing 149 on the support member 148 toprevent lateral movement of the blades 22, 24 and support member 148from the recess 122.

[0064] The actuator support 124 (FIG. 8) extends from the frame 62 andincludes a pair of fingers 125 spaced apart forming a clevis. Theactuator support 124 pivotally receives a mounting portion 164 (FIG. 3)of the actuator 88 between the fingers 125. Thus, the actuator 88 ispivotally fixed to the frame 62 at one end. The actuator 88 includes arod 166 (FIG. 14) extending therefrom in a direction opposite to themounting portion 164.

[0065] The rod 166 is fixed to a piston 168 (FIG. 17A) for reciprocalmovement within a cylindrical chamber 182 in the actuator 88. The piston168 divides the chamber 182 into a variable volume “open” chamber 184and a variable volume “cut” chamber 188. When fluid flow under pressureis directed into the open chamber 184 through port 186 and fluid ispermitted to exhaust from cut chamber 188, the greater pressure withinthe open chamber forces the piston 168 and rod 166 to move axially tothe right in a blade open direction, as viewed in FIG. 17A. The rod 166moving in a blade open direction, moves the blade 24, through the drivelink 102, in a direction towards the fully open position, as illustratedin FIG. 2. When fluid pressure is directed into the “cut” chamber 188through port 190, and fluid exhausts from the cut chamber 184, thepiston 168 and rod 166 are forced to move to the left in a blade cutdirection, as viewed in FIG. 17A. The rod 166 moving in a blade cutdirection moves the blade 24, through the drive link 102, towards thefully closed position, as illustrated in FIG. 1. The actuator 88 islocated relative to the frame 62 and sized to fit comfortably within thepalm of a hand of an operator of the shears 20. The actuator 88 providessufficient force to cut items, such as small chicken bones.

[0066] The servo control valve 84, (FIGS. 3, 16 and 17A-H) is receivedin the valve chamber 128 which extends completely through the frame 62.The servo control valve 84 is operably coupled to the actuator 88 byfluid conducting lines 222, 224 (FIGS. 3, 4 and 17A). The lines 222, 224may be located internal or external of the frame 62. Preferably, thelines 222, 224 are external with the line 222 fitting in a groove in thethumb handle portion 64 facing away from the blades 22, 24. The optionalsafety valve 86 is received in the valve chamber 129 which extends onlypartially through the frame 62.

[0067] An optional safety lever 202 (FIG. 5) is pivotally supported inthe thumb handle portion 64 of the frame 62 about a pin 204. A button206, at the end of one relatively long leg portion of the safety lever202, extends into the thumb opening 142 of the thumb handle portion 64under bias of the safety valve 86. When an operator inserts a thumb intothe thumb opening 142, the button 206 is depressed and the lever 202pivots about the pin 204.

[0068] A relatively short end portion 208 of the lever 202 moves a rod210 (FIGS. 5 and 16) in the safety valve 86 to a position permittingfluid pressure from a fluid inlet 211 to the servo control valve 84through a passage 212. When the button 206 is not depressed, a checkvalve 216 in the safety valve 86 is biased by a spring 217 to block theflow of pressurized fluid to the passage 212 and the servo control valve84. This assures that fluid pressure is applied to the actuator 88 tomove the blade 24 only when an operator has a thumb in the thumb opening142 in the thumb handle portion 64 of the frame and can control theshears 20. This optional feature, although shown, is omitted in thepreferred embodiment to eliminate a risk that can occur in the event ofan interruption in power while the blades are in an open relationship.Without power, the blades will remain open upon the moving of the fingerloop 66 to a closed position, which could occur through carelessness orinadvertence, notwithstanding that the loop is spring biased to an openposition. In the event of such an occurrence, if the safety lever 202 isoperated when the power is returned, the open blades will immediatelysnap shut, creating a potential danger believed greater than thatprotected by the safety lever.

[0069] A cutting or shearing action is effected during closure of theblade 24 relative to the blade 22 from the position illustrated in FIG.2 to the position illustrated in FIG. 1. The blade 22 is pivotablerelative to the frame 62 about the member 148 and the axis AA. The blade22 is pivotable in response to movement of the loop handle 66 relativeto the frame 62. When the shears 20 are in the fully closed position, asillustrated in FIG. 1, the blades 22, 24 overlie one another in aside-by-side engaged relationship.

[0070] The pivotable blade 22 is illustrated in FIG. 10 in detail. Thepivotable blade 22 includes an opening 242 extending through the bladeand sized to closely fit over the member 149. The pivotable blade 22includes a relatively long cutting portion 244 extending from theopening 242 and having the cutting edge 42 formed thereon. The pivotableblade 22 includes an actuating portion 246 extending from the opening242 in a direction away from the cutting portion 244, at an obtuse angleB relative to a straight unground edge portion 247 located directlybelow the opening 242 and contiguous with the cutting edge 42. Theobtuse angle B is in the range of 120° to 170°, and is preferably 144°.

[0071] The extent E1 of the actuating portion 246 from the center of theopening 242 is less than the extent E2 of the cutting portion 244 fromthe center of the opening. The ratio of the extent E2 of the cuttingportion 244 to the extent E1 of the actuating portion 246 is in therange of between one to one (1:1) to ten to one (10:1), and preferablyis 4.9:1. The extent E2 of the cutting portion 244 is preferably 5inches from the center of the opening 242 to the tip of the blade. Theextent E1 is preferably 1.006 inches from the center of the opening 242to an end surface 249 of the actuating portion.

[0072] The actuating portion 246 of the blade 22 includes an elongatedslot 248 opening through the end surface 249 and extending in adirection toward the opening 242. The slot 248 is defined by twoparallel side surfaces 250, 252 extending in a direction substantiallyparallel to a line extending from the center of the opening 242 at anangle of 144° relative to the unground edge portion 247. The actuatingportion 246 also has a pair of substantially parallel extending surfaces254, 256 extending in a direction parallel to the slot 248 defining sidesurfaces 250, 252 of the actuating portion. The slot 248 accepts adriving member 258 (FIGS. 14 and 15) of the drive link 102 to force theblade 22 to pivot relative to the fixed blade 24 upon pivoting of thedrive link. A heel 284 is located on the actuating portion 246 oppositethe opening 242 from the cutting portion 244. The heel 284 includes aride surface 288 on the blade 22. The fixed blade 24 is illustrated indetail in FIGS. 11-13. The fixed blade 24 includes an opening 280, acutting portion 282 and a mounting end 290. The opening 280 is formed toclosely receive a portion of the support member 148 and 149. The supportmember 148, blade surfaces 150 and 150B and frame surfaces 152, 154cooperate to prevent movement of the blade 24 relative to the frame 62(FIG. 6). The cutting edge 44 of the fixed blade 24 is formed in thecutting portion 282 by grinding and/or polishing. The cutting edge 44has a straight portion adjacent the mounting end 290 and a distal endportion having a slight curvature; for example, a radius in the range of30-200 inches. The cutting portions 244, 282 of the respective blades22, 24 are slightly bowed away from one another between their tips andrespective openings 242, 280. An alternative fixed blade 24A (FIG. 11A)includes a ball tip 286 at the end of cutting portion 282A, which aidsin eviscerating animal carcasses.

[0073] The mounting end 290 (FIGS. 12 and 13) of the fixed blade 24 islocated relative to the opening 280 diametrically opposite to thecutting portion 282. The mounting end 290 has a portion 287 bentupwardly, as viewed in FIGS. 12 and 13, during manufacture of the blade24 away from a lower side surface 292 of the blade, as viewed in FIGS.12 and 13. This deformed portion 287 of the mounting end 290 assuresthat the bent portion 287 extends in a direction parallel to the upperside surface 294, but offset. The bent portion 287 of mounting endportion 290 preferably extends 0.010 inch from the upper side surface294 of the blade 24. The bent portion 287 of mounting end 290 ispreferably ground flat after the deforming operation in order to form asurface generally parallel with the upper side surface 294 of the blade24.

[0074] An alternate mounting end 290A (FIG. 13A) of the fixed blade 24A(FIG. 11A) is located relative to the opening 280 diametrically oppositeto the cutting portion 282. The mounting end 290A has a portion 287Adeformed upwardly, as viewed in FIG. 13A, during manufacture of theblade 24A away from a upper side surface 294 of the blade, as viewed inFIG. 13. This deformed portion 287A of the mounting end 290A is formedby engaging a lower side surface 292A extending in a direction parallelto the upper side surface 294A with a punch to form recess 289. Thedeformed portion 287A of mounting end portion 290A is forced by thepunch and preferably extends 0;010 inch from the upper side surface 294Aof the blade 24A. The deformed portion 287A of mounting end 290A ispreferably ground flat after the deforming operation in order to form asurface generally parallel with the upper side surface 294A of the blade24A,

[0075] The ride surface 288 (FIG. 10) of the pivotable blade can beinterchanged with either raised surface 287 or 287A (FIGS. 13 & 13A) ofthe fixed blade, as preferred to suit the manufacturing process. Theseare mating features which cooperate to bias the cutting edges of theblades together.

[0076] The cutting edges 42, 44 are adapted to face one another when theblades are properly installed in the frame 62. When the blades 22, 24are relatively pivoted towards one another, the deformed portion 287 ofthe mounting end 290 of the fixed blade 4 engages the ride surface 288in the heel 284 of the pivotable blade 22. The engagement between thedeformed portion 287 and the ride surface 288 assures that the cuttingedges 42, 44 are continuously biased towards one another to contact andto create a moving cutting point during closure of the blade 22 relativeto the blade 24.

[0077] Another mounting arrangement between a modified fixed blade 24Band a modified frame 62B of the shears 20B is illustrated in FIGS. 19,20 and 26. The mounting arrangement between replaceable blades 22B, 24Band the frame 62B is secure and reliable, yet facilitates easyreplacement, when the blades are to be changed.

[0078] The modified frame 62B has a thumb recess 64B rather than acomplete encirclement for the thumb, and employs a strap 62C thatextends across the back of the hand of an operator. Also, the safetyvalve 86 is omitted and a passage 86A extends within the frame,communicating with a cross passage 212B through which fluid underoperating pressure is supplied directly to the servo valve 84. Themechanism for operating the blades is otherwise the same as describedwith respect to the embodiment utilizing the frame 62.

[0079] The modified frame 62B includes a pair of load bearing pins 63fixed to and extending transversely from a cavity portion 65 of theframe. The load to bearing pins 63 are located on substantiallydiametrical opposite sides of the axis AA about which the blade 22Bpivots, offset only slightly as indicated at Q1 at FIG. 19 forstructural convenience from a precise diametrically oppositerelationship. The fixed blade 24B includes a mounting portion 290B thathas a substantially planar surface 291 (FIG. 20). The fixed blade 24Bincludes a pair of openings 67A, 67B formed in its mounting portion290B. One opening 67A is substantially circular and tightly fits aboutthe exterior of one pin 63. The other opening 67B is elongated into agenerally oval or elliptical shape with a width that tightly fits aboutthe other pin 63 and a length that is greater than the diameter of thepin. This elongated opening 67B allows for some manufacturing tolerancesin the placement of the openings and/or the pins 63. The wide spacing ofthe pins 63 and the openings 67A, 67B and their relationship to thepivot axis AA and their fit with the pins 63, results in effectiveanchoring of the blades and prevents movement of the fixed blade 22B.

[0080] The load bearing pins 63 withstand the majority of the loadapplied between the blades and frame during operation of the blades 22B,24B as these blades act against a workpiece. The widely spaced pins 63,acting as a couple, bear the shearing load between the blades, and avoidthe use of a relatively small edge surface of a blade to engage a partof the frame 62B to absorb such load.

[0081] The replaceability and interchangeability of the blades 22B, 24Bor other working members as an assembled unit is an important feature ofthe shears or tool of the present invention. For example, a straightblade assembly is illustrated in FIG. 20. The blades 22B, 24B each havea cutting edge 42B, 44B that is essentially straight along its entirelength of approximately 4.00 inches to 4.50 inches. When the cuttingedges 42B, 44B of these blades 22B, 24B wear, become dull, otherwisedamaged or when the type of blade is required to be changed, they caneasily be replaced by closing the blades, loosening a blade screw 292(FIG. 20) that extends along the axis AA and which connects the bladesto a threaded opening 293 in the frame 62B and removing the blades as aunit by lifting them off of the pins 63.

[0082] For safety, the removal or replacement of the blades 22B, 24Brequires that the blades be in a closed position relative to oneanother. To insure that the blades 22B, 24B are closed during removal orinstallation, a portion 297, crescent shaped in the embodiment shown,forms a part of the actuating portion 264B of the pivotable blade 22B.When the pivotable blade 22B of an installed pair is in a position otherthan the relatively closed position, this crescent shaped portion 297will be located in an open area of the frame 62B, indicated at 298 (FIG.20), behind and below a frame portion 299 that interferes withinstallation and removal of the blades in other than a closed condition.This will be clear from FIG. 19. The pivotable blade 22B must be in itsclosed position relative to the fixed blade 24B for the crescent shapedportion 297 to be located out of the area 298 formed in the modifiedframe 62B. This relative location of the crescent shaped portion 297 outof the slot 298 permits the movement of the blades in a directionparallel to the extent of the pins 63. A replacement set of blades 22B,24B can then be installed or the blades can be serviced or sharpened andthen reinstalled.

[0083] The blades 22B, 24B are fastened together as a unit by a pivotingassembly (FIG. 20A) which includes a lock nut 294, blade washer 295,pivot nut 296 and the blade screw 292. The lock nut 294 and pivot nut296 interengage along a threaded portion 294A to maintain the blades22B, 24B together while also permitting pivotal action relativetherebetween. The blade screw 292 extends through both the lock nut 294and pivot nut 296. A threaded portion 292A is received in the opening293 to maintain the blades 22B, 24B in the frame 62B and on the pins 63.A smaller diameter nonthreaded portion 292B is located within the locknut 294 and pivot nut 296 to allow the screw to move freely whileengaging or disengaging the thread portion of the Frame 293. Thisfeature allows the screw to remain captured within the blade set whenthe set is removed from the frame, pivoting of the blade 22B. The pivotnut 296 has a “D” shaped boss 296P on its exterior portion to fit withina “D” shaped opening 296D the fixed blade 24B to prevent relativerotation between the pivot nut and the fixed blade 24B.

[0084] The replaceable blade unit includes the straight blade assemblyillustrated in FIGS. 19A and 20, which has relatively straight cuttingedges 42B, 44B and a relatively blunt end 299B on the fixed blade 24B.The pivotable blade has a curved end portion with a pointed end 299P(See FIG. 20) The cutting edges 42B, 44B cooperate to shear a workpieceby engaging along a line of contact that is contained in a planeextending substantially parallel to the planar surface 291.

[0085] As illustrated in FIGS. 21 and 21A a modified version of thereplaceable blade unit is illustrated. The blade unit includes apivotable blade 22C with a pointed end 299CP. A fixed blade 24C has ablunt end 299CB. The blades 22C, 24C engage along a path curved relativeto the planar surface 291C of the fixed blade 24C, as illustrated inFIG. 21A. This curvature can be “right hand” as shown, or opposite (notshown).

[0086] As illustrated in FIG. 22, another replacement blade unitincludes a fixed blade 24D having a ball tip 299BT. The ball tip 299BTpermits the fixed blade 24D to be inserted into a narrow channel in theworkpiece without cutting or digging into the surface. A pivotable blade22D includes a relatively sharp pointed end 299PE which can be used topuncture a product or workpiece.

[0087] A replaceable blade unit illustrated in FIG. 23 is designated a“gizzard” blade assembly. The fixed blade 24G has a relatively sharppointed end 299GB to impale a product or workpiece. The pivotable blade22G has a squared end 299GS. As illustrated in FIG. 24 a replaceableblade unit is a straight short blade assembly. The blades 22F, 24F arerelatively shorter than the blades 22B, 24B illustrated in FIG. 20. Thefixed blade 24F has a raised blunt end 299BE. A replaceable blade unitillustrated in FIG. 25 is described as a “neck breaker” blade assembly,The blades 22B, 24B are relatively thick, taken in the direction ofrelative pivotal movement and, thus, are relatively strong in thatdirection. These blades are typically used for breaking bones in apoultry workpiece such as a chicken or turkey. The neck breaker bladeassembly has its pivotal blade 22G with a removable anvil edge 22AE. Theanvil edge 22AE is relatively wide, taken in a direction normal to thedirection of relative pivotal movement. This blade 22G cuts by forcingthe work product against and into a sharp edge 245E of the fixed blades24G as the blunt anvil cutting edge and the sharp cutting edge arebrought into mutual contact crushing when the moveable anvil edge 22AEis brought into engagement with a sharp edge 24SE of the fixed blade24G. Such a forceful engagement between the two blades can also be usedby other working members such as a power operated crimping tool withsuitable crimping edges.

[0088] The drive link 102 is a bell crank member having a generalL-shape. As illustrated in FIGS. 14 and 15, the drive link 102 isconnected for pivotable movement about the pin 134. The pin 134 isreceived in the openings of the frame 62 and is located approximatelyalong the longitudinal center line of the fixed blade 24. The drive link102 pivots in the frame 62 at a location between the rod 166 of theactuator 88 and the slot 248 of the pivotable blade 22. A relativelylonger leg 302 of the drive link 102 is connected with the rod 166 by apin 306. The distance between the centers of the pins 134 and 306 ispreferably 1.24 inches, The relatively shorter leg 304 of the drive link102 is connected with the actuating portion 246 of the pivotable blade22. The linkage between the leg 304 and the slot 248 of the pivotableblade 22 is through the pin and roller 258, which is in rollingengagement with the blade. The distance between the centers of the pins258 and 134 is preferably 0.83 inch.

[0089] The ratio of the distances of the longer leg portion 302 to theshorter leg portion 304 is in the range of 1.15:1 to 1.85:1 and ispreferably about 1.50:1. This “leg ratio” being greater than 1.0provides an increase in force transmitted to the actuating portion 246of the blade 22 compared to the force applied to the drive link 102 bythe rod 166. This force multiplication due to the mechanical advantageprovided by the drive link 102 enables a relatively large cutting forceto be applied between the blades 22, 24, Concurrently, a decrease inangular travel of the blade 22 compared between the angle of travel ofthe long leg 302 occurs as the blade is closing. The decreasing angulartravel produces a proportionately increasing amount of force applied toblade 22, which compensates in part for the drop in cutting force thatoccurs as the cut point moves toward the end of the blade.

[0090] Pivotable movement of the drive link 102 about the pin 134 pivotsthe blade 22 about axis AA through engagement of the blade by the pin258 in the slot 248. For example, when the rod 166 of actuator 88 isforced to move axially to the left, as viewed in FIG. 15, the longer legportion 302 of the drive link 102 pivots clockwise about the pin 134causing the leg portion 304 to follow with clockwise pivotal movementabout the pin. However, the arcuate movement at pin 258 is less than thearcuate movement at pin 306. This results because the distance from thecenters of pin 134 to pin 258 is less than the distance from the centersof pin 134 to the center of pin 306. To accommodate the pivoting of theblade 22 and the link 102, while keeping the construction compact, theslot 248 begins at least within 0.55 inch from the axis AA and extends adistance of at least 1.0 inch from the axis AA.

[0091] The finger loop handle 66 is received in the recess 120 in theframe 62. The finger loop handle 66 pivots relative to the support 118about the same axis AA as the blade 24 pivots. The finger loop handle 66pivots about 20° to 25° relative to the frame 62 between the fully openposition illustrated in FIG. 2, and the fully closed positionillustrated in FIG. 1, or about half of the arcuate movement of thepivotable blade 22. The finger loop handle 66 includes a finger handleportion 322 for receiving therein up to four fingers of an operator'shand located opposite the thumb. The finger handle portion 322 ispreferably continuous and closed which allows an operator's fingers tomove the loop handle 66 in both directions for pivotable movement aboutthe support 118, and also acts as a guard for the fingers.

[0092] A pivot portion 320 of the loop handle 66 surrounds the support118 and is narrower than the width of the finger handle portion 322. Thereturn spring 226 engages an end surface 326 on pivot portion 320 of thefinger loop handle 66 to continuously bias the finger loop handleportion 322 towards the fully open position, as illustrated in FIG. 2.

[0093] A blade link 340 (FIG. 14) forms a part of the feedback linkage104. The blade link 340 is also received on the support member 118 atopening 338 for pivotable movement about the axis AA. The blade link 340is located in the recess 120 of the frame 62. The blade link 340 isaxially offset from the pivot portion 320 of the loop handle 66.

[0094] The blade link 340 detects movement of the pivotable blade 22 andcommunicates that movement to a difference link 362 in the feedbacklinkage 104. The blade link 340 detects movement of the pivotable blade22 at one end by engagement with the pin 258 in the drive link 102 thatextends through a slot 342 of the blade link. The movement of the bladelink 340 is transmitted to the difference link 362 through a pin 344 ata location relative to the opening 338 which is generally opposite theslot 342. The distance from the axis AA at which the pin 258 engages asurface defining the slot 342 of the blade link 340 is in the range of0.73 to 0.96 inch. The distance to the center of the pin 344 from theaxis AA is 0.46 inch. The pin 258, thus, moves through an arcuatedistance greater than the arcuate distance that the pin 344 moves and isproportionately greater by a ratio in the range of about 1.5:1 to about2.1:1.

[0095] The difference link 362 is connected between the pin 344 of theblade link 340 and a pin 366 on the finger loop handle 66. Thedifference link 362 forms part of the feedback linkage 104 andcommunicates a difference between pivotal movement of the blade 24 andthe pivotal movement of the finger loop handle 66 to the servo controlvalve 84.

[0096] The difference link 362 is a generally L-shaped member formed bylegs 374, 376 meeting at an apex. A pin 382 in an aperture 370 at theapex communicates movement of the apex to an actuator link 386 of theservo valve 84. The difference link 362 includes a slot 364 in leg 374for receiving the pin 344 of the blade link 340 and an opening 368 inthe leg 376 for receiving the pin 366 of the finger loop handle 66. Thedistance from the center of the opening 368 in one leg 376 of thedifference link 362 to the center of the aperture 370 at the apex isshorter than the distance between the center of the aperture 370 to theaverage center of the slot 364 in the other leg 374. The difference link362 has a ratio of the length of leg 374 to the length of leg 376 in therange of about 1.3:1 to 1.7:1. Thus, a relatively larger proportion ofmovement of the finger loop handle 66 is communicated to the servocontrol valve 84 than the proportion of movement of the pivotable blade22.

[0097] The offset distance of the aperture 370 from a line from thecenters of openings 368 and slot 364 on link 362 results in a decreasein speed of movement as the blade 22 nears the closed position. Thisdecrease in speed of movement of the blade 22 relative to the movementof the handle 66 is represented by curve 300 in FIG. 18 as “blade gainratio.” The blade gain ratio is plotted as a function of the anglebetween the blades 22, 24. This noticeable gain ratio means that thechange in angle between the blades 22, 24, to the change in anglebetween the handle 66 and the frame 62, decreases from over a 6:1 ratioat the fully open position to about 1:1 at the closed position. This iscompared to the constant 1:1 ratio of conventional scissors in curve310. The variable “blade gain ratio” is particularly advantageous forcontrolling cutting with a relatively slow closure rate near the fullyclosed blade position.

[0098] A pin 382 received in the aperture 370 at the apex of thedifference link 362 extends into an opening 384 of the actuator link386. The actuator link 386 includes an opening 388 at an end opposite tothe opening 384. The opening 388 receives a pin 390 that is connectedwith a stem 400 in the servo control valve 84.

[0099] The actuator link 386 transmits motion of the difference link 362to the stem 400 in the servo control valve 84. Because the differencelink 362 reflects the difference in pivotal movement between the loophandle 66 and the pivotable blade 22 and moves the actuator link 386and, hence, the stem 400 in the servo control valve 84, it provides adifference feedback signal to the servo control valve.

[0100] For example, the finger loop handle 66 is pivoted by an operatorfrom the open position to the closed position nearer the frame 62 whenthe blades 22, 24 are in the fully open position, as illustrated in FIG.2. The difference link 362 then pivots clockwise about the pin 344 bythe pin 366 in the finger loop handle 66. The pin 382 forces theactuator link 386 to move the stem 400 axially inward within the servocontrol valve 84, in a direction that causes the pivotable blade 22 tomove towards the closed position. There is a time lag before the piston168 and the power rod 166 of the actuator 88 force the pivotable blade22 to pivot towards the closed position that is illustrated in FIG. 1.During this time lag, until the blade 22 begins to pivot, the differencelink 362 has pivoted only about the pin 344 supported in the blade link340. Once the blade 22 begins to pivot, the position of the differencelink 362 then reflects a tendency to pivot about pin 366. If the fingerloop handle 66 continues to move ahead of the blade 22 movement, thenmovement of pins 366, 344 tend to cancel their influence on thedifference link 362 and produce an apparent rotation about pin 382. Theactuator link 386 essentially maintains its position and the blade 22continues to pivot. If the blade 22 movement tends to catch up to thefinger loop handle 66 movement, the difference link 362 pivots about pin366, causing the actuator link 386 to move the stem 400 in a directionaxially out of the valve 84, reducing the flow of fluid to the actuator88 and, hence, showing or stopping pivoting of the blade 22.

[0101] Thus, the servo control valve 84 is actuated from the positionillustrated in FIG. 17A through the position illustrated in FIGS. 17Bthrough 17D by movement of the difference link 362. The travel limit ofthe stem 400 within the servo control valve 84 is illustrated in FIG.17D. During the axial inward movement or cut signal, indicated by thearrow 396 (FIG. 16), of the stem 400 within the servo control valve 84,fluid is directed to the line 222 to the port 190 and into the “cut”chamber 188 in the actuator 88. This forces the piston 168 and itsassociated rod 166 to move in a cut direction and move the blade 22 fromthe open position towards the closed position. The rod 166 forces thedrive link 102 to pivot the pivotable blade 22 toward the fixed blade 24with a cutting action.

[0102] During this pivotable movement of the pivotable blade 22 towardsthe fixed blade 22, the blade link 340 communicates the movement of thepivotable blade to the difference link 362. The difference link 362pivots about the pin 366 in a clockwise direction which causes theactuator link 386 to pull the stem 400 in a direction axially outward ofthe servo control valve 84. The pivotable blade 22 tries to catch up tothe desired position indicated by the position of the finger loop handle66 relative to the frame 62. The difference link 362 continues to pivotclockwise about the pin 366. The pivotable blade 22 does eventuallycatch up to the desired blade position indicated by the position of theloop handle 66 relative to the frame 62.

[0103] The difference link 362 detects that the position of thepivotable blade 22 relative to the blade 24 or frame 62 has caught up tothe desired position indicated by the position of the loop handle 66relative to the frame 62. The difference link 362 stops rotating abouteither pin 366 or 344. No motion is, thus, imparted to the actuator link386 and the stem 400 is in a “neutral” position, illustrated in FIG.17G, which does not cause any further pivoting of the blade 22 from theposition it was in when the stem reached the neutral position. It willbe apparent that from the position that the blade 22 stopped, it couldthereafter be opened, closed or could remain stationary relative to theblade 24, as long as the blade 22 is between the fully open or fullyclosed positions when it stopped moving.

[0104] To move the blade 22 towards the open position of FIG. 2, thereverse takes place. The loop handle 66 is pivoted away from the frame62 towards the fully open position illustrated in FIG. 2. This forcesthe pin 366 to pivot the difference link 362 at opening 368counterclockwise about the pin 344. This pivoting motion of thedifference link 362 imparts a force to the actuator link 386 that pullsthe control stem 400 in a direction axially outward of the servo controlvalve 84 towards the position illustrated in FIG. 17H.

[0105] Such axially outward motion causes fluid to flow through line 224to port 186 and into open chamber 184. Fluid pressure forces the piston168 and rod 166 to move in a direction towards the mounting portion end164 of the, actuator 88. This axially inward movement of the rod 166 inthe actuator 88 causes the drive link 102 to pivot in a clockwisedirection about the pin 134 which causes the actuating portion 246 ofthe blade 22 to pivot about the axis AA in a counter-clockwisedirection. Pivoting of the drive link 102 in a clockwise directioncauses the blade 22 to move from the closed position illustrated in FIG.1 relative to the fixed blade 24 toward the open position illustrated inFIG. 2.

[0106] Thus, the stem 400 moves from the position in the servo controlvalve 84 illustrated in FIG. 17G progressively to the positionillustrated in FIG. 17H. The position illustrated in FIG. 17H is areversing travel position or a position in which opening motion of theblade 22 will occur.

[0107] The servo control valve 84 (FIG. 16) controls fluid flow to theactuator 88. The servo control valve 84 includes a valve body 422 thatdefines an elongated chamber 424. Two oppositely facing pistons 426, 428are independently movable longitudinally within the chamber 424 of thevalve body 422. Each piston 426, 428 has an inner annular first valveseat 442 and an outer annular first obturating surface 444. Areciprocable valve stem 446 extends through and is at least partiallysurrounded by the pistons 426, 428. The valve stem 446 is connected toand is part of stem 400. Each of the pistons 426, 428 includes a surface447 for transmitting force to the piston in a direction away from theother. The servo control valve 84 may optionally include a compressionspring 445 between and acting concurrently against the forcetransmitting surface 447 associated with each piston 426, 428.

[0108] Two oppositely facing spaced annular second obturating surfaces448 are carried by the valve stem 446 at opposite ends a fixed distanceD1 apart. The pistons 426, 428 are located between the two secondobturating surfaces 448 and are reciprocable relative to the valve stem446. Each of the second obturating surfaces 448 are arranged tocooperate with one of the inner annular first valve seats 442 to controlfluid flow along the valve stem 446 from the fluid inlet 212intermediate the pistons 426, 428.

[0109] Two annular second valve seats 462 are fixed in the valve body422. Each of the second valve seats 462 is located to coact with theouter annular first obturating surfaces 444 of one of the pistons 426,428. This contact limits the longitudinal movement of the pistons 426,428 in a direction away from each other and controls fluid flow past theouter annular first obturating surfaces 444.

[0110] A first port 482 to the chamber 424 is located between thepistons 426, 428 and serves as a fluid inlet to the chamber. A secondport 484 and a third port 486 are for separate fluid communication withthe chambers 184, 188 through lines 222, 224, respectively. The secondport 484 and the third port 486 communicate independently with a commonpassage 488 in the frame 62 for exhausting fluid from the servo controlvalve 84 and shears 20 at exhaust port 129. The second port 484 andthird port 486 are associated with a respective one of the second valveseats 462 for exhausting fluid from the chambers 184, 188. The secondport 484 is closable by the right piston 426, as viewed in FIG. 16, toblock fluid flow from the chamber 188 to the common passage 488. Thethird port 486 is closable by the left piston 428, as viewed in FIG. 16,to block fluid flow from the chamber 184 to the common passage 488.

[0111] A fourth port 502 and a fifth port 504 to the chamber 424 areeach located longitudinally outward of the pistons 426, 428 and theirassociated second valve seats 462. The fourth port 502 is for supplyingfluid to and receiving fluid from the “cut” chamber 188 of the fluidactuator 88. The fifth port 504 is for supplying fluid to and receivingfluid from the “open” chamber 184 of the fluid actuator 88. The distanceD1 between the two second obturating surfaces 448 and the distance D2between the two annular second valve seats 462 are such that the pistons426, 428 permit limited fluid flow or a “controlled leakage” from thefirst port 482 equally to the fourth port 502 and fifth port 504 whenthe valve stem 446 is in the “neutral” or first position. The distancesD1 and D2 are also such that the pistons 426, 428 allow preferentialfluid flow through the fourth port 502 or the fifth port 504 and onlyone of the second port 484 and the third port 486 when the valve stem446 is in a position other than the first position. It should beapparent that the distances D1 and D2 may be established so that thepistons 426, 428 completely block fluid flow to the fourth port 502 andthe fifth port 504 when the valve stem 446 is in the first position.

[0112] Operation

[0113] The description will relate to the shears 20 and blades 22, 24but is equally applicable to the use of the shears 20B, modified frame62B and blades 22B, 24B, and any other of the blades or work membersoperable by the disclosed mechanism, To operate the shears 20 embodyingthe present invention the following procedure is followed. Assuming thatthe operator desires to cut something, such as cloth, paper, cardboardor meat, the shears 20 will normally start with the blades 22, 24 in thefully open relative position illustrated in FIG. 2. To move the blades22, 24 from the open position illustrated in FIG. 2 to the closed endingposition illustrated in FIG. 1, the operator first inserts a thumb intothe thumb opening 142 in the thumb handle portion 64 in the frame 62. Asthe operator's thumb is fitted in the opening 64, the safety button 206if provided, is depressed to permit pressurized fluid to pass throughthe safety valve 86 and into the servo control valve 84. In thepreferred embodiment, the button, safety lever 202 and safety valve 86are omitted and pressurized fluid passes directly to the control valve84. At least one of the operator's fingers is received in the fingerhandle portion 322 in the finger loop handle 66. The operator thenmanually pivots the finger loop handle 66 from the open positionillustrated in FIG, 2 towards the closed position illustrated in FIG. 1.The operator may stop the pivoting movement of the finger loop handle 66anywhere between the open and closed position or continue to the travellimit or closed position, illustrated in FIG. 1.

[0114] This starting of relative pivoting action of the finger loophandle 66 forces the difference link 362 to pivot about the pin 344 in aclockwise direction (FIG. 14) and forces the actuator link 382 to movethe stem 400 axially inward of the servo control valve 84 from theposition illustrated in FIG. 17A to the position illustrated in FIG.17B. This motion of the stem 400 allows fluid to flow to “cut” chamber188 of the actuator 88 through port 502 which moves the piston 168 in adirection to move the rod 166 axially outward of the actuator. That is,the conical surface 448 disengages from the valve seat 442 on piston 426to communicate the first port 482 with the fourth port 502 to allowfluid flow to the “cut” chamber 188. Concurrently, the left port 504fluidly communicates with the third port 486 to exhaust fluid from the“open” chamber 184. The second port 484 is maintained blocked by piston426. Thus, the drive link 102 pivots counterclockwise about the pin 134and drives the pivotable blade 22 towards the fixed blade 24.

[0115] Upon further pivoting movement of the finger loop handle 66relative to the frame 62, but before the blade 24 catches up to theposition indicated by the finger loop handle, the difference link 362pivots further about the pin 344 in a clockwise direction. This causesthe stem 400 to be moved farther inward of the servo control valve 84from the position illustrated in FIG. 17B to the position illustrated inFIG. 17C. The conical surface 448 is spaced further from the valve seat442 on piston 426 and the piston 428 is spaced further from annularvalve seat 462, than the position illustrated in FIG. 17B. This allowsrelatively more fluid flow between the first port 482 and the fourthport 502 and between the fifth port 504 and third port 486. The greaterfluid flow to the cut chamber 188 of the actuator 88 forces the piston168 and rod 166 to pivot the blade 22 even faster towards the closedposition.

[0116] The maximum cut position of the servo control valve 84 isillustrated in FIG. 17D. This position is reached by pivoting the fingerloop handle 66 quickly towards the frame 62 while cutting a toughobject. The difference link 362 pivots clockwise about the pin 344 tomove the stem 400 to its axial inward limit. The conical surface 448 isspaced a maximum distance from the seat 442 of the piston 426 and thepiston is held against the annular valve seat 462 by fluid pressure inthe chamber 424. Concurrently, the surface 444 of the piston 428 isspaced from the annular vale seat 462. This position permits the maximumfluid flow between the first port 482 and the fourth port 502 andbetween the fifth port 504 and third port 486. This flow moves the blade22 quickly and with maximum force, to cut the tough object.

[0117] When the pivoted position of the blade 22 begins to catch up withthe position indicated by the finger loop handle 66, the difference link362 begins to pivot about the pin 366 due to movement of the pivotableblade relative to the position of the finger loop handle. The differencelink 362 causes the stem 400 to move axially outward of the servocontrol valve 84 to the position illustrated in FIG. 17E from theposition illustrated in FIGS. 17C or 17D. The conical surface 448 movescloser to the piston 426 and the piston 428 moves closer to the valveseat 462. Fluid flow from the first port 482 to the fourth port 502 andfrom the fifth port 504 to third port 486 continues but at a reducedrate. The blade 22 still is forced to close but at a slower closurerate.

[0118] The cutting action of the blades 22, 24 can be stopped at anytime by stopping the finger loop handle 66 at any position between itstravel limits. The blade 22 will then stop at a position correspondingto the relative position of the finger loop handle 66. This will causethe difference link 362 to maintain a neutral position in which fluidpressure, applied to either chamber 184, 188 of the actuator 88, is notincreased.

[0119] To open the shears 20 from the position illustrated in FIG. 1towards the position illustrated in FIG. 2, the operator manually pivotsthe loop handle 66 away from the frame 62. The difference link 362pivots counterclockwise about the pin 344 to force the actuator link 386to pull the stem 400 outwardly of servo control valve 84. This actionprovides fluid flow from the control valve to the open chamber 184 inthe actuator 88. Fluid pressure in chamber 184 forces the power rod 166to move axially inward into the actuator 88 and causes the drive link102 to pivot clockwise about the pin 134. This imparts a force to pivotthe blade 22 counterclockwise about the axis AA in a direction towardsthe open position relative to the fixed blade 24.

[0120] When the difference link 362 pivots counterclockwise about thepin 344, the stem 400 is caused to move axially outward of the servocontrol valve 84 from the position illustrated in FIG. 17E to theposition illustrated in FIG. 17F. The right conical surface 448 engagesthe piston 426 to block fluid flow to the “cut” chamber 188 through thefourth port 502. The second port 484 remains blocked by the piston 426.The left conical surface 448 disengages the piston 428 to allow fluidflow to the “open” chamber 184 through the fifth port 504. The thirdport 486 is closed by the piston 428. Pressure in the chambers 184 and188 equalizes on either side of the piston 168 to stop movement of therod 166 and blade 22.

[0121] The difference link 362 and stem 400 are returned to theirrespective neutral positions. The stem 400 is centered in the servocontrol valve 84 in the first position again, as illustrated in FIG. 17Gwhich is the same as FIG. 17A. Equal fluid flow, or no fluid flow,occurs from the first port 482 to the fourth port 502 and fifth port504. Exhaust to the second and third ports 484, 486 is permitted ifneeded,

[0122] If the blade 22, during a cutting action, overshoots the desiredposition indicated by the finger loop handle 66, the servo control valve84 can compensate, as illustrated in FIG. 17H. The difference link 362pivots clockwise about the pin 366 due to the excessive movement of theblade 22, The stem 400 is moved axially outward of the servo controlvalve 84 to the position illustrated in FIG. 17H. The piston 426 isspaced from the annular valve seat 462 to permit fluid flow from the“cut” chamber 188 through the fourth port 502 to exhaust through thesecond port 484. The piston 426 engages conical surface 448 to blockfluid flow from the first port 482. At the same time, the piston 428engages the annular valve seat 462 but is spaced from the left conicalsurface 448. This blocks fluid flow to exhaust through the third port486 while permitting fluid flow from the inlet first port 482 to theopen chamber 184 through the fifth port 504. This flow causes the piston168 and rod 166 to move inward of the actuator 88 to stop and reversethe cutting action of the pivotable blade 22.

[0123] Other uses than the power operated shears are also contemplatedfor the tool of the present invention. For example, the tool can beused, without limitation, as power operated pliers, crimpers, clamp,caulking gun or other tool in which it is desirable to have reversible,controllable, force multiplied and/or slower speed at the end ofrelative movement between members.

[0124] Thus, while preferred embodiments of the invention have beendisclosed, various modifications and alterations can be made theretowithout departing from the spirit and scope of the invention set forthin the appended claims.

Having described a preferred embodiment of the invention, we claim:
 1. Apair of replaceable blades for a hand-held power-operatedblade-actuating device, said blades without handles and havingcooperating edges for cutting, said pair of blades comprising a firstblade having a cutting portion and having a mounting portion by whichthe first blade can be fixed relative to a support and a second bladehaving a cutting portion and an actuating portion and constructed to bepivoted relative to the support and the first blade at a location on thesecond blade between the cutting portion of the second blade and theactuating portion of the second blade, a surface forming a part of theactuating portion for operatively coupling the second blade to a poweredactuator, the actuating portion of said second blade including a portionthat is located relative to the mounting portion of the first blade whenthe blades are closed to allow attachment and removal of the blades asan assembled unit to or from the support, and located when the bladesare open to prevent the attachment or removal of the blades to or fromthe support, and a locating surface on the pair of assembled blades thatextends transversely of the general extent of the blades for engagingwith a surface of the support that extends transversely of the generalextent of the blades when the blades are mounted on the support.
 2. Apair of blades as set forth in claim 1 including a heel portion forminga part of the actuating portion of the second blade substantiallyaligned with the cutting edge of the second blade and having a ridesurface facing toward the first blade, a surface on the first bladeopposed to and contacted by the ride surface to bias the cutting edge ofone blade into mutual contact with the cutting edge of the other bladeat a location along each where the cutting edges intersect.
 3. A pair ofblades as set forth in claim 2 wherein one of said ride surface andopposed surface has a portion projecting toward the other from thegeneral plane of the respective blade to bias the cutting edge of oneblade into mutual contact with the cutting edge of the other blade at alocation along each where the cutting edges intersect.
 4. A pair ofblades as set forth in claim 1, 2 or 3 wherein said coupling surface isformed by a slot in which a movable drive portion associated with anactuator is receivable, said slot extending at an obtuse angle withrespect to the general extent of the cutting edge of the second bladeand beginning at least within 0.55 inch from the location of the pivotof the second blade and extending a distance of at least 1.0 inch fromthe location of the pivot.
 5. A pair of blades as set forth in claim 1wherein said mounting portion has an opening to receive a load bearingpin of the support and serves to inhibit relative movement between saidfirst blade and the support.
 6. A pair of blades as set forth in claim 5including a second opening in the mounting portion, said first andsecond openings being located substantially diametrically opposite toeach other relative to the location where the second blade pivotsrelative to the first blade, to inhibit relative rotation of the firstblade with respect to the support.
 7. A pair of blades as set forth inclaim 1, 2, 3, 5 or 6 in which the actuating portion of the second bladeincludes a portion that underlies the mounting portion of the firstblade when the blades are closed and that extends from behind themounting portion when the blades are not closed, and when extendingprevents the attachment or removal of the blades to or from the support.8. A pair of replaceable work members for a hand-held power-operatedwork member-actuating device, said work members without handles andhaving cooperating work surfaces for pressing against a work piecelocated between the two work members, said pair of work memberscomprising a first member having a working portion and a mountingportion by which the first member can be fixed relative to a support anda second member having a working portion and an actuating portion andconstructed to be pivoted relative to the support and the first memberat a location on the second member between the working portion of thesecond member and the actuating portion of the second member, a surfaceforming a part of the actuating portion for operatively coupling thesecond member to a power-operated actuator, the actuating portion ofsaid second member including a portion that is located relative to themounting portion of the first member when the work surfaces are closedto allow attachment and removal of the members as an assembled unit toor from the support, and located when the members are open to preventthe attachment or removal of the members to or from the support, and alocating surface on the pair of assembled members that extendstransversely of the general extent of the mounting and actuatingportions of the members for engaging with a surface of the support thatextends transversely of the general extent of the mounting and actuatingportions of the members when the members are mounted on the support. 9.A pair of work members as set forth in claim 8 including a heel portionforming a part of the actuating portion of the second work membersubstantially aligned with the work surface of the second work memberand having a ride surface facing toward the first work member, a surfaceon the first work member opposed to and contacted by the ride surface tobias the work surface of one work member into mutual contact with thework surface of the other work member at a location along each where thecutting edges intersect.
 10. A pair of work members as set forth inclaim 9 wherein one of said ride surface and opposed surface has aportion projecting toward the other from the general plane of therespective work member to bias the work surface of one work member intomutual contact with the work surface of the other work member at alocation along each where the cutting edges intersect.
 11. A pair ofwork members as set forth in claim 8, 9 or 10 wherein said couplingsurface is formed by a slot in which a movable drive portion associatedwith an actuator is receivable, said slot extending at an obtuse anglewith respect to the general extent of the work surface of the secondwork member and beginning at least within 0.55 inch from the location ofthe pivot of the second work member and extending a distance of at least1.0 inch from the location of the pivot.
 12. A pair of work members asset forth in claim 8 wherein said mounting portion has an opening toreceive a load bearing pin of the support and serves to inhibit relativemovement between said first work member and the support.
 13. A pair ofwork members as set forth in claim 12 including a second opening in themounting portion, said first and second openings being locatedsubstantially diametrically opposite to each other relative to thelocation where the second work member pivots relative to the first workmember, to inhibit relative rotation of the first work member withrespect to the support.
 14. A pair of work members as set forth in claim8, 9, 10, 12 or 13 in which the actuating portion of the second workmember includes a portion that underlies the mounting portion of thefirst work member when the work members are closed and that extends frombehind the mounting portion when the work members are not closed, andwhen extending prevents the attachment or removal of the work members toor from the support.
 15. A hand-held power-operated tool, said toolcomprising: first and second members for performing a desired task uponrelative movement about a pivot axis from a first position towards asecond position, said first member having a mounting portion and saidsecond member having an actuating portion; a frame for supporting saidmembers in extending relationship to the frame for relative pivotalmovement; a load bearing pin extending from said frame and spaced fromthe pivot axis of said members; an opening in the mounting portion ofsaid first member to receive said pin; a thumb-receiving recess in theframe; a finger-operated control member secured to the frame, relativelymovable with respect to the first and second members and the frame, saidcontrol member extending from the frame in a direction generallyopposite to that of said second member, and said thumb-receiving recessbeing located on said frame at a position generally aligned with anddisplaced from said first member; an actuator engaged with the actuatingportion of said second member for moving said second member relative tosaid first member; and a servo mechanism controlled by said secondmember and said finger-operated control member that controls operationof said actuator to move said second member relative to said firstmember in response to movement of said finger-operated control member.16. A tool as set forth in claim 15 including a second load bearing pinextending from said frame and spaced from the pivot axis of said membersand a second an opening in the mounting portion of said first member toreceive said second pin, said two pins and two openings being locatedsubstantially diametrically opposite to each other relative to the pivotaxis.
 17. A tool as set forth in claim 15 or 16 including a recess inthe frame in which the actuating portion of the second member moves whenthe second member is pivoted with respect to the first member, and asurface at least in part bounding an opening to the recess, said openingbeing a size and shape that said surface allows entry or removal of thesecond member to the recess when the members are pivoted to a closedposition and prevents entry or removal when the first and second membersare displaced from a closed position.